Symptoms of an Over Active Thyroid in Cats

Hyperthyroidism, a disease where the thyroid is over active, is one of the most common endocrine conditions affecting cats over the age of ten years. Some veterinarians estimate that about 5 to 10 percent of middle to old-aged cats will develop hyperthyroidism and, because of factors that many include environmental exposures, that number is on the rise. The good news is that this disorder is a very treatable disease; most hyperthyroid cats will make a complete recovery, usually following iodine treatment for cats.


1. Weight loss. This is the classic and most common sign of hyperthyroidism, despite a normal to increased appetite. The weight loss associated is usually progressive and is usually first noticed by the owner as a loss of muscle mass around the cat’s back.

2. Increased appetite. Sometimes an increase in appetite can be dramatic, with some cats doubling the amount of food eaten. Hyperthyroid cats eat more in an attempt to compensate for their abnormally higher metabolic rate by increasing the calories they ingest.

3. Hyperactivity. This is particularly exhibited as restlessness or nervousness. In extreme hyperthyroidism, muscle tremor or twitching may be apparent, and are usually described to have an anxious or frantic expression. These are often noticeable to the examining physician.

4. Increased thirst and urination. About half of cats with hyperthyroidism will show signs of increased thirst (polydipsia) and urination (polyuria). Veterinarians mostly refer to these simply as PU/PD.” The most common cause of these symptoms is mild, concurrent kidney disease.

5. Vomiting or regurgitation. Gastrointestinal signs are common among cats with hyperthyroidism. It appears to be common among cats in multi-cat households and mostly occurs shortly after feeding. During the early stages, this can be solved by giving your cat small, frequent meals.


6. Anxiety. The behavioral sign most obvious to owners is night yowling. Aimless pacing and easily interrupted sleep patterns may also occur in some hyperthyroid cats. All these are associated with the increased central nervous stimulation caused by hyperthyroidism.

7. Diarrhea. Soft stools and diarrhea can occur in about a third of cats with hyperthyroidism. Other cats develop large voluminous stools with frequent defection. It is likely that accelerated gastrointestinal transit contributes to these symptoms. Some cats also develop malabsorption.

8. Skin, coat and nail changes. The hair coat, especially in long-haired breeds, is often unkempt, dull and may even be matted. Some cats may groom excessively resulting in alopecia or military dermatitis. Excessive nail growth can occur, especially among cats with chronic hyperthyroidism.

9. Apathetic hyperthyroidism. A small percentage of hyperthyroid cats show atypical signs where restlessness is replaced by depression. Although weight loss is present in these cats, it is accompanied by poor appetite. This heightens the importance of a high index of suspicion.

Your cat does not have to have to all these clinical signs and symptoms to have an overactive thyroid problem. But if your cat has one or more of these signs, especially if he is older than ten years of age, you should have your cat tested for hyperthyroidism in a pet referral hospital. This way, treating hyperthyroidism in cats can be started as soon as possible.

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